High Pressure Chemistry Of Phenyl Radical Reactions With Acetylene
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The formation of polycyclic aromatic hydrocarbons (PAHs), especially fused-ring compounds, represents an essential step in the mechanisms of soot formation. In particular the second-ring species, naphthalene, plays a key role as a building block for the subsequent growth to larger PAHs. Nevertheless the pathways leading to naphthalene are still uncertain requiring further experimental and theoretical investigations. In the present work the pyrolytic reactions of the phenyl radical in the presence of acetylene have been studied as a possible pathway to the formation of the second-ring species. The experimental work has been conducted using the single-pulse high-pressure shock tube (HPST) at the University of Illinois at Chicago. A new experimental set-up, for use with the HPST, was studied and developed for accurate measurement of large compounds. The major stable species obtained from the experimental work, including the heavy polycyclic aromatic hydrocarbons, were identified and measured using gas chromatography/mass spectrometry techniques. The experiments were performed over a wide range of high-pressures (25 – 50 atm) and temperatures (900 – 1800 K) which encompass typical conditions in modern combustion chambers. The experimental results on both the phenyl pyrolysis and the phenyl + acetylene reactions provide unique data about these reaction systems. In fact, for the first time, it has been possible to detect and accurately measure a variety of PAH compounds, including the fused-ring species, for which mole fraction profiles have been obtained. Such species profiles were utilized to develop and validate a comprehensive chemical kinetic model which helped clarify aspects related to the mechanisms involved in the formation of large polycyclic aromatic hydrocarbons at high pressures. In addition, in order to explore new possible pathways for the formation of condensed structures, a theoretical study of the radical/π-bond addition reactions between single-ring aromatic hydrocarbons was performed using ab-initio quantum mechanics calculations. Several pathways leading to the formation of PAH compounds have been addressed as potentially relevant for typical combustion environments.
polycyclic aromatic hydrocarbons